CHROMATE REMOVAL FROM WATER USING SURFACTANT-ENHANCED CROSS-FLOW FILTRATION

Removal of chromate from water was investigated using the surfactant e nhanced crossflow filtration technique in which the cationic surfactan t, cetyl trimethylammonium bromide (CTAB), was the carrier for the met al ions. The variation of chromate and surfactant rejections, and perm eate flux with time were measured as a function of CTAB/chromate conce ntration ratio, while maintaining a constant transmembrane pressure dr op, membrane pore size, and pH of the feed solution. The method was fo und to be effective in removing chromate from water. It was observed t hat the efficiency of chromate removal increased with increasing CTAB/ chromate ratio. It was also found that the chromate concentration had a significant effect on the CTAB concentration in the permeate and on the time taken to establish the secondary membrane which consists of a highly viscous surfactant phase in the hexagonal state in the absence of chromate. In the presence of chromate, permeate flux increased at the same CTAB concentration although the surfactant and chromate rejec tions decreased, indicating lowering of the secondary membrane resista nce to permeate flow. These conclusions were confirmed by dead-end fil tration experiments which showed that the fouling index decreased by t he addition of chromate while the opposite was valid when sodium chlor ide was present in the surfactant/water/electrolyte ternary system.